1. Field of the Invention
The present invention relates to a sheet feeder for feeding a sheet in a predetermined direction and an image forming apparatus provided with such a sheet feeder.
2. Description of the Related Art
An image forming apparatus such as a copier, a printer or a facsimile machine includes an image forming unit for forming an image on a sheet and a sheet feeder for feeding a sheet to the image forming unit.
For example, according to a first technology, a sheet feeder includes, as main constituent elements, a sheet cassette for storing sheets, a feed roller for feeding a sheet in the sheet cassette to an image forming unit, and a retard roller arranged to face the feed roller while being held in contact therewith to prevent simultaneous feed of plural sheets. In the sheet feeder of the first technology, an inserting direction of the sheet cassette into a housing of the image forming apparatus is the same as a feeding direction of a sheet to the image forming unit by the feed roller.
Since a remaining amount of sheets in the sheet cassette decreases as sheets are fed to the image forming unit, it needs to be notified to a user. A member for detecting the remaining amount of sheets is known according to a second technology.
A remaining amount detecting member of the second technology includes a sensor piece held in contact with the uppermost one of sheets in a sheet cassette, a photosensor which is a photointerrupter, and a light shielding piece for shielding light from the photosensor. Since the light shielding piece is constructed to rotate according to a height position of the sensor piece in a vertical direction, its rotation amount changes according to the remaining amount of sheets in the sheet cassette. An amount of the light to be shielded is determined according to the rotation amount of the light shielding piece, and the remaining amount of sheets in the sheet cassette is judged according to the amount of the shielded light.
If the remaining amount detecting member as disclosed in the second technology is applied to the sheet feeder of the first technology, it may be damaged. Specifically, if the sensor piece of the remaining amount detecting member of the second technology is formed to come into contact with the uppermost one of the sheets in the sheet cassette in a direction opposite from the inserting direction of the sheet cassette into the housing of the image forming apparatus, i.e. if the inserting direction of the sheet cassette into the housing and a contacting direction of the sensor piece with the uppermost sheet are opposite to each other, the sensor piece is easily caught by a side wall of the sheet cassette or the uppermost sheet when the sheet cassette is inserted into the housing. If being caught by the uppermost sheet, the sensor piece may be damaged. If this occurs, the remaining amount of sheets in the sheet cassette cannot be accurately detected.